The aim of the proposed study is to interrelate precisely steroid hormone receptor containing cells to the peptidergic and aminergic system in rat brain. This will be studied by immunohistochemistry and by combined autoradiography and immunohistochemistry. The ontogeny of estrogen receptor containing cells in fetal brain at different times of development will be determined by immunohistochemistry, using monoclonal receptor antibodies. The effects of progesterone on intracellular distribution of estradiol receptor will be assessed. Neurons containing both estradiol and progesterone receptors will be identified using estradiol receptor antibody for immunostaining and 3H ORG2058, a synthetic progestin for nuclear uptake of radioactivity. A double immunostaining procedure will be applied to interrelate estrogen receptor containing cells to peptide or neurotransmitter producing cells. Specifically an attempt will be made to determine the interaction between pro-luteinizing hormone releasing hormone (GnRH associated peptide, GAP) producing neurons and estrogen receptor containing neurons as well as neurotransmitter systems. Effects of estradiol on levels of preproenkephalin and proopiomelanocortin mRNAs in certain populations of brain neurons will be determined by in situ hybridization histochemistry utilizing cDNA or cRNA to preproenkephalin and proopiomelanocortin. Study on colocalization of 3H ORG2058 and antibodies to neuropeptides will be conducted for the characterization of progestin target cells. The results of this study will help in understanding the role of steroid hormones in the central regulation of neuroendocrine function and behavioral response.